How often do you workout? And how long have you been doing this?

For those of you that are used to exercising on a regular basis, how do you stick with it? I try to workout a few times each week, but i'd like to do more. Summer always motivates me to kick up my workout regimen; however, I find I have a problem sticking with a routine. I feel like if I can get past those initial weeks, then I will be able to keep it up on a regular basis with no problems. What drives you to keep going? Even on those days where you've been at work all day and don't want to do anything?